Thermally stable jet fuel

ABSTRACT

THERMALLY STABLE JET FUEL IS PRODUCED BY CONTACTING A JET FUEL WITH A CATALYST COMPOSITION COMPRISING FROM 15 TO 25 WEIGHT PERCENT OF A GROUP VI METAL AND FRM 15 TO 25 WEIGHT PERCENT OF A GROUP VIII METAL COMPOSITED WITH A HALOGEN ECRICHED ALUMINA SUPPORT UNDER HYDROGENATION CONDITIONS.

United States Patent 1 ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION In the operation of jet engines it is important that the jet fuel be thermally stable as it is circulated through a heat exchanger in indirect heat exchange with the oil from the engine. If the jet fuel contains thermally unstable constituents, the heat exchangers, screens, and nozzles in the fuel system. will become clogged with such constituents in the form of polymeric materials. The formation of such undesirable products 'dueto the thermal unstability of the jet fuel will result in malfunctioning of the jet engine;

a In establishing specifications for jet fuels a concerted effort has .been made to obtain a test procedure for defining jet fuels that minimize deposit formation due to thermal instability in the operation of jet aircraft. A test found suitable for measuring the thermal stability of jet fuels is the CRC fuel coker test set forth as ASTM D 1660-70. a I

In the production of jet fuels selected segregated refinery streams boiling in the naphtha and kerosene range are normally employed. These fuels having a substantial parafiinic concentration are not normally stable enough for use in supersonic aircraft due to the very high heat stability required forsuch operation. It has been found to be necessary to subject such refinery streams to stabilizing, processes such as severe acid treating to obtain a thermally stable fuel for such supersonic aircraft. These acid treating processes are not economically feasible, result in substantial product loss, and are therefore unsuited for commercial plant production.

A second method for the preparation of thermally stable jet fuels involves hydrogenation of the fuel in the presence of a catalyst such as cobalt molybdate, molybdenum disulfide, o'rmolybdena supported on alumina where the total concentration of metals is normally in the range of 5-25 Weight percent of the catalyst composition. This conventional hydrogenation step has been found to be ineffective to produce supersonic jet fuels which have necessarily high thermal stability requirements. In the production of such supersonic jetfuels, it has been necessary heretofore to employ a two stage hydrogenation process where in a second hydrogenation step a catalyst composition' comprising a relatively high concentration of a Group VIII metal such as nickel on a support such as alumina is utilized. l

Accordingly, an object of the invention is to provide an improved process for the production of jet fuels having a high thermal stability.

Another object of the invention is to provide a process for the production of thermally stable supersonic jet fuels.

Yet another object of the invention is to provide an improved single stage hydrogenation process for the production of jet fuels having a high thermal stability.

, 3,824,181 Patented July 16, 1974 Other objects, advantages and features of the invention will be readily apparent to those skilled in the art from the following description and appended claims.

SUMMARY OF THE INVENTION By the invention an improved process for the production of thermally stable jet fuels is provided whereby a jet fuel feed is contacted with a catalyst comprising from 15 to 25 weight percent of a Group VI metal and from 15-25 weight percent of a Group VIII metal composited with a halogen enriched alumina support under severe hydrogenation conditions.

DESCRIPTION OF THE INVENTION It has been discovered that thermally stable jet fuels can be prepared by treating selected hydrocarbon distillates boiling in the range of ZOO-600 F. (93-316 C.) with hydrogen in the presence of a particularly defined catalyst composition. The invention is particularly applicable to the preparation of thermally stable jet fuel compositions prepared by the hydrogenation of a hydrocarbon distillate boiling in the range of 300-500 F. (149- 288 C.).

The catalyst composition employed in the process of this invention contains from 15-25 Weight percent of a hydrogenation metal component selected from Group VI- B and from 15-25 weight percent of at least one hydrogenating metal component selected from Group VIII of the Periodic Table. Catalyst compositions found to be particularly effective in the practice of this invention are those in which the hydrogenating metal components are tungsten and nickel.

The hydrogenation components are composited with an alumina support. The alumina support employed in the preparation of the catalyst composition of this invention will contain less than 2.0 weight percent impurities such as silica. In addition to the hydrogenating components and alumina, the catalyst compositions of this invention also contain a combined halogen usually in an amount of 0.5 percent to about 10.0 percent by weight of the total catalyst and preferably about 1.0 to 4.0 percent by weight. A catalyst composition found to be particularly effective in the practice of this invention comprises an alumina supported catalyst containing 20.0 Weight percent tungsten, 20.0 weight percent nickel and 2.0 weight percent fluorine.

The catalyst compositions of this invention can be prepared by processes known in the art. In a typical catalyst preparation procedure the alumina support, such as extruded alumina pellets which have been previously calcined, can be admixed with tungsten which is in the form of any Water soluble compound of tungsten, the tungsten being present as the anion. Ammonium salts of tungstic acid and particularly ammonium metatungstate, ammonium tungstate or ammonia silica-dodecatungstate can be employed in the impregnation procedure. The halogen can be added to the catalyst composite as a solution of ammonium salt with the tungsten or by a separate impregnation step. As previously indicated], the concentration of tungsten in the finished catalyst should be in the range of 15-25 percent by weight and the concentration of the halogen should be in the range of 0.5 to 10 percent by weight. The wet impregnated alumina can then be dried at, for example, a temperature of 250 F. (121 C.) for a period of time ranging from about 4 to about 24 hours. Following drying the alumina impregnated with tungsten can be calcined.

Thereafter, the alumina can be contacted with an aqueous solution of the Group VIII metal salt such as the nitrate, sulfate, or chloride. Alternatively, salts of organic acids such as acetate, formate or propionate can be utilized. Sufi'iicient salt is admixed with an aqueous support so as to provide a catalyst composite containing from -25 percent by weight of the Group VIII metal such as nickel. The wet catalyst composite can then be dried in a second drying step, such as the time and temperature described in connection with the first drying step. Following the drying step the catalyst composite can then be calcined at a temperature in the range of 800-1600 F. (427-871" C.) for a period of 1-24 hours.

Although a two-step impregnation catalyst preparation procedure has been described, it is within the skill of the art and the scope of this invention to employ a single impregnation step in adding the hydrogenation metals to the alumina support. Other conventional methods for compositing the hydrogenation metals and halogen with the alumina support can be employed. If a second Group VIII metal is to be employed in the catalyst composite, this second Group VIII hydrogenation metal can be impregnated simultaneously with the first Group VIII hydrogenation metal employing the procedure previously described.

When the use of the catalyst in the sulfided form is desired, the catalyst composite can be presulfided after calcination, or after calcination and reduction.

The single-stage hydrogenation reaction for the production of a thermally stable jet fuel eifected pursuant to the process of this invention can be conducted at a temperature in the range of 500-800 F. (260427 0.), preferably, 550750 F. (287-398" C.). The hydrogenation process is conducted by contacting the catalyst composite with the jet fuel feed in the presence of uncombined hydrogen partial pressures in the range of 1500- 4000 p.s.i.g. (105.5-282 kg./cm. The hydrogenation reaction can be continuously conducted in the liquid or vaporous phase and at a liquid volume hourly space velocity in the range of 0.25-10, preferably 2.0-4.0. Reaction zone pressures in the range of 1500500 p.s.i.g. (105.5-352 kg./cm normally in the range of 2000- 4000 p.s.i.g. (140.5-282 kg./cm. are maintained in the hydrogenation zone.

Hydrogen is circulated through the hydrogenation reactor at a rate between 2000-15,000 standard cubic feet (56.60425 cubic meters) per barrel of feed with the hydrogen purity varying from 60-100 percent. With recirculation of the hydrogen, it may be necessary to provide for bleeding off a portion of the recycled gas and to add hydrogen as makeup in order to maintain the hydrogen purity within the range specified. If desired, the recycled gas can be washed with a chemical absorbent for hydrogen sulfide or otherwise treated in a conventional manner to reduce the hydrogen sulfide content thereof prior to recycling.

The jet fuel product of the single stage hydrogen step is thermally stable as determined by the aforementioned CRC Fuel Coker Test Method set forth in ASTM D 1660-70. The thermal stability of the jet fuels produced by the novel hydrogenation process is accomplished without the necessity of employing conventional two-stage jet fuel thermal stability processes. Furthermore, the thermal stability of the single-stage hydrogenation process of this invention is greater than that of some jet fuels produced by conventional two-stage processes.

The following examples are presented to illustrate objects and advantages of the invention. It is not intended, however, that the invention should be limited to the specific embodiments presented therein.

EXAMPLE 1 In this example a catalyst composite comprising 20.0 weight percent tungsten, 20.0 weight percent nickel and 2.0 Weight percent fluorine on an alumina support was employed in the single stage hydrogenation of a jet fuel feed characterized as follows:

,TABLE 1 Gravity, API 41.2 Aniline Pt., F 146 (63 C.) Luminometer No. (ASTM D 1740) 47 Smoke Pt. (ASTM D 1322) 22 Distillation, (ASTM D 86): it

10% condensed at, F. 406 (208 C.) 90% condensed at, F. 463 239 C.)

Net Heat of Combustion, B.t.u./Lb. 18,'549

Freezing Pt., F. (ASTM D 1477) 54 C.)

The above-characterized jet fuel feed was-subjected to a single-stage hydrogenation in three runs employing the process conditions shown below in TableII.

for each of the runs was inspected and the results of the tests shown below in Table III:

TABLE III Run 1 Run 2 Run 3 Gravity, API" 43. 7 43. 5 44. 1 Aniline pt., F"..- 164.4 163. 3 163.5 Luminometer number. 74 74 69 Smoke point 33 33 30 Thermal stability (ASTM D 1660-7): l

Preheater deposit 2 2 2 Filter AP, inches mercury. 0 0 0 Distillation, 10% condensation p F. 406 392 402 Net heat of combustion, B.t.u./lb 18, 673 18, 664 18, 675 Freezing point, F e 52 54 I -53 B Fuel prestrcsscd for 3 hours at 300 F. (149 0.), test conducted at 200 p.s.i.g. (14.1 kgs./cm.2) and at a rate of 2.5 1b./hr. (1.14 kgsJhr.) for 5 hours at 600 F. (315 C.) preheater and 600 F. (315 C.) filter temperatures.

208 C. 200 C. 205" C. -47 C. -48 G.

Acceptable preheater deposit rating should not exceed 2.0 and filter AP should not exceed 3.0 in determining thermal stability acceptability of the jet fuel. By these standards, each of the jet fuel products of Runs 1, 2 and 3 have an acceptable thermal stability.

EXAMPLE 2 In this example a catalyst composite comprising 6.0 weight percent nickel and 19.0 weight percent tungsten impregnated on an alumina support was employed in the single stage hydrogenation of a jet fuel feed characterized as follows:

TABLE IV Gravity, API 42.9 Aniline Pt., F. 147 (64 C.) Luminometer No. (ASTM D '1740) 55 Smoke Pt. (ASTM D 1322) 25 Distillation (ASTMD 86): 1 I

10% condensed at, F. 384 (195 C.) 90% condensed at, F. 457 (236 C.)

'Iwo runs (Runs 4 and 5) were made employing the above identified jet fuel feed utilizing a single-stage hydrogenation process employing the process conditions shown below in Table V.

TABLE V Run 4 Run 5 Operating conditions:

Total reaction pressure, p.s.i.g 2, 2, 135 Space velocity, liquid volume hourly 3.0 1.5 Average catalyst bed temperature, F- 698 652 Hydrogen partial pressure, p.s.i.gd 2, 122 '2, 128 Hydrogen circulation rate, s.c.f./barrel 2, 134 4, 157

kgJcmfi. 370 C. 344 C. 3 149 kgJcmJ. Q 150 kgJemfl.

l Test conducted at 200 p.s.i.g. (14.1 kgsJcmfl) and a. rate of 2.5 lbJ hr. (1.14 kgs./hr.) for 5 hours at 550 F. (288 C.) preheater and 650 F. (343 C.) filter temperatures.

b 198 C. 201 C. 238 C. I 239 C.

From the above, it is apparent that with preheater deposit ratings of 3 and 4, respectively, the product of Runs 4 and 5 is not thermally stable employing the standard discussed in Example 1.

EXAMPLE 3 In this example the necessity for employing a two stage hydrogenation process for the production of a thermally stable jet fuel is demonstrated when employing a conventional jet fuel hydrogenation catalyst. The catalyst employed in the initial stage comprises 6.0 weight percent nickel and 19.0 weight percent tungsten impregnated on an alumina support. The catalyst composition employed in the second hydrogenation stage comprised 48.0 weight percent nickel deposited on kieselguhr. The kerosene feed to the first hydrogenation stage was the same as the feed in Example 2.

In the first hydrogenation stage the jet fuel feed was passed through the catalyst bed at a space velocity of 3.0 liquid volumes per hour per volume of catalyst, with a pressure of 2135 p.s.i.g. (150 lags/cm?) maintained in the reaction zone. The average temperature in the reaction zone was 698 F. (370 C.). A hydrogen partial pressure of 2032 p.s.i.g. (1'43 kgs./cm. was maintained in the hydrogenation zone. Hydrogen of 92.6 11101 percent purity was passed at the rate of 2479 standard cubic feet per barrel through the first hydrogenation stage reaction zone.

The product withdrawn from the first hydrogenation stage had the following characteristics:

TABLE VII Gravity, API 44.6 Flash Point, PM (ASTM D 93) 152 Freezing Point, F. (ASTM D 1477) 59 (-50 C.)

Smoke Point, Mm. (ASTM D 1322) 38 Luminometer No., (ASTM D 1740) 76 Distillation, F. (ASTM D 86):

90%, F 460 (238 C.) Thermal Stability, 5 hrs.

(Modified ASTM 1660-70):

Fuel Flow: lbs/hr. a- 2.5 Preheater Temp., F. 550 (288 C.) Filter Temp., F. 650 (343 C.) Heater Deposit Code 3 6 through the reaction at 2000 scf./bbl. The feed was passed through the second hydrogenation reactor at a space velocity of 1.50 liquid volumes/hour/volume of catalyst. The product withdrawn from the second hydrogenation stage had the following characteristics:

TABLE VIII Gravity, API 45.1 Flash Point, PM (ASTM D 93) 156 Freezing Point, F. (ASTM D 1477) 61 (-52 C.) Smoke Point, Mm. (ASTM D 1322) 37 Luminometer No., (ASTM D 1740) Distillation, F. (ASTM D 86):

90%, F. 461 (238 C.) Thermal Stability, 5 hrs.

(Modified ASTM 1660-70):

Fuel Flow: lbs/hr 3.0

Preheater Temp., F. 700 (371 C.)

Filter Temp., F. 800 (427 C.)

Heater Deposit Code 2 As discussed in Example 1, the preheater deposit rating should not exceed 2.0. It is apparent from the above that a single hydrogenation stage was ineffective to obtain a jet fuel product of acceptable thermal stability. Only after the product from the first hydrogenation stage was subjected to a second hydrogenation stage was a product of acceptable thermal stability obtained.

Although the invention has been described with reference to specific embodiments, references, and details, various modifications and changes will be apparent to one skilled in the art and are contemplated to be embraced in the invention.

We claim:

1. A process which comprises contacting in a hydrogenation zone a jet fuel feed with a catalyst consisting essentially of from 15 to 25 weight percent of a Group VI metal and from 15 to 25 weight percent of a Group VIII metal composited with an alumina support containing from 0.5 to 10 Weight percent halogen, maintaining a temperature in the range of 500 to 800 F. and a pressure of 1500 to 5000 p.s.i.g. in said hydrogenation zone, passing hydrogen to said hydrogenation zone at the rate of 2000 to 15,000 standard cubic feet per barrel of jet fuel feed, maintaining a hydrogen partial pressure in the range of 1500 to 4000 p.s.i.g. in said hydrogenation zone, maintaining a space velocity in said hydrogenation zone in the range of 0.25 to 10 liquid volumes/hour/ volume of catalyst, and recovering therefrom a thermally stable jet fuel product.

2. The process of Claim 1 wherein said hydrogenation process is conducted in the range of 550 to 750 F. and at a liquid volume hourly space velocity in the range of 2.0 to 4.0.

3. The process of Claim 2 wherein said Group VI metal is tungsten and said Group VIII metal is nickel.

4. The process of Claim 3 wherein said halogen is fluorine.

5. The process of Claim 1 wherein said catalyst consists essentially of 20.0 weight percent nickel, 20.0 weight percent tungsten, 2.0 weight percent fluorine and alumina.

References Cited UNITED STATES PATENTS 3,369,998 2/ 1968 Bercik et a1. 208-143 3,477,963 11/1969 Van Venrooy 208-143 3,527,693 9/ 1970 Barnes et a1 208--143 CURTIS R. DAVIS, Primary Examiner UNITED STATES PATENT omen CERTIFICATE OF CORRECTION mm No.' 3.824.;181 mm! July 16, 1974 Inventofl's) Harry C. Stauffer, Robegic A. Titmgg 5 James R, Murphy It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected u shown below;

Colume 3, line 38, "1500 500" should sead --l500 '5000- Colume 4, line 24, ,"The above-characterized jet fuel feed was subjected" should read -The product of the single-stage hydrogenation process Colume 6, line. l, "reaction" should read --reactor-- Signed and sealed this 8th day of October 1974.

( SEAL Attest:

McCOY'M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents I 

